It is known that photovoltaic cells absorb photon energy from sunlight and use specially prepared semiconductor junctions to convert part of the energy thus received to electricity.
It is also known that a specific photovoltaic semiconductor junction can utilize, for conversion to electricity, only a portion of the spectrum of photon energy available. For example, the conversion of sunlight to electrical energy using well known silicon photovoltaic cells is strongly dependent upon the conversion of light with energy around 1.1 electron volts, while some of the lower energy light also present is not converted to electricity but rather to heat. The heat generated can reduce the efficiency of the silicon cell.
Accordingly, current photovoltaic cells receive more energy input from incident light than they convert into electrical output, and it is highly desirable to increase the amount of light energy an array retains for such conversion.
One known approach for increasing the capacity of photovoltaic cells to convert a wider spectrum of photon energies to electricity is to employ one or more luminescent agents which, when exposed to sunlight, absorb the higher energy light and in response emit lower energy light. Examples of such agents are organic dyes such as the dyes heretofore employed in the scintillation counters, lasers, and the like.
The particular luminescent agent or agents employed in conjunction with a specific photovoltaic cell are chosen, inter alia, for their ability to produce light of an energy level which best suits the conversion characteristics of that cell. This way, a portion of the higher energy light that would otherwise not be utilized by the cell for electrical generation is transformed by the luminescent agent into lower energy light that the cell can readily convert into electricity, thereby increasing the efficiency of the cell.
A photovoltaic array which employs this approach is referred to as a luminescent photovoltaic array. Such an array usually employs fluorescent dyes, fluorescence being that species of luminescence wherein the emitted light is usually in the visible spectrum. However, other species of luminescence exist, for example, phosphoresence where light emission continues after the stimulating light has stopped.
It should be understood that this invention applies to all species of luminescence, as well as to all types of luminescent agents.